The importance of automatic identification systems increases particularly in the service sector, in the field of logistics, in the field of commerce and in the field of industrial production. Further applications of identification systems are related to the identification of persons and animals.
In particular contactless identification systems like transponder systems (for instance using an RFID tag) are suitable for a wireless transmission of data in a fast manner and without cable connections that may be disturbing. Such systems use the emission and reflection/absorption of electromagnetic waves, particularly in the high frequency domain. For a normal contactless smart card transaction the terminal starts to send a message to request all present cards to provide a response. During the initialization phase all cards provide an identification code that allows the terminal to distinguish the cards and address them individually.
Pseudo random identifiers are known from ISO/IEC 14443 Type B.
Fixed and unique as well as random identifiers are known from ISO/IEC 14443 Type A.
Since all the commands and responses during the initialization phase may be sent in plain text, (unencrypted) fixed and unique identifiers impose a certain risk to be misused for unauthorized tracking purposes, something that is frequently called privacy problem.
Random identifiers resolve any privacy issue and are therefore mandated by many applications because they are generated randomly after each power-up of after each reception of a REQUEST command.
Hence, conventional transponder-based communication systems may be not safe enough to ensure privacy. Moreover, a reliable performance of such systems may not be guaranteed under undesired circumstances such as a sudden interruption of a communication connection between a transponder and a reader device.